Revert "RISC-V: mm: Document mmap changes"

This mmap behavior caused unintended breakages so the behavior has been
changed.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20240826-riscv_mmap-v1-1-cd8962afe47f@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: charlie-rivos

Documentation/arch/riscv/vm-layout.rst

@@ -134,19 +134,3 @@ RISC-V Linux Kernel SV57
    ffffffff00000000 |  -4     GB | ffffffff7fffffff |    2 GB | modules, BPF
    ffffffff80000000 |  -2     GB | ffffffffffffffff |    2 GB | kernel
   __________________|____________|__________________|_________|____________________________________________________________
-
-
-Userspace VAs
---------------------
-To maintain compatibility with software that relies on the VA space with a
-maximum of 48 bits the kernel will, by default, return virtual addresses to
-userspace from a 48-bit range (sv48). This default behavior is achieved by
-passing 0 into the hint address parameter of mmap. On CPUs with an address space
-smaller than sv48, the CPU maximum supported address space will be the default.
-
-Software can "opt-in" to receiving VAs from another VA space by providing
-a hint address to mmap. When a hint address is passed to mmap, the returned
-address will never use more bits than the hint address. For example, if a hint
-address of `1 << 40` is passed to mmap, a valid returned address will never use
-bits 41 through 63. If no mappable addresses are available in that range, mmap
-will return `MAP_FAILED`.